191fcdb6c9
The following crash happens for me when running the -mm selftests (below). Specifically, it happens while running the uffd-stress subtests: kernel BUG at mm/hugetlb.c:7249! invalid opcode: 0000 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 3238 Comm: uffd-stress Not tainted 6.4.0-hubbard-github+ #109 Hardware name: ASUS X299-A/PRIME X299-A, BIOS 1503 08/03/2018 RIP: 0010:huge_pte_alloc+0x12c/0x1a0 ... Call Trace: <TASK> ? __die_body+0x63/0xb0 ? die+0x9f/0xc0 ? do_trap+0xab/0x180 ? huge_pte_alloc+0x12c/0x1a0 ? do_error_trap+0xc6/0x110 ? huge_pte_alloc+0x12c/0x1a0 ? handle_invalid_op+0x2c/0x40 ? huge_pte_alloc+0x12c/0x1a0 ? exc_invalid_op+0x33/0x50 ? asm_exc_invalid_op+0x16/0x20 ? __pfx_put_prev_task_idle+0x10/0x10 ? huge_pte_alloc+0x12c/0x1a0 hugetlb_fault+0x1a3/0x1120 ? finish_task_switch+0xb3/0x2a0 ? lock_is_held_type+0xdb/0x150 handle_mm_fault+0xb8a/0xd40 ? find_vma+0x5d/0xa0 do_user_addr_fault+0x257/0x5d0 exc_page_fault+0x7b/0x1f0 asm_exc_page_fault+0x22/0x30 That happens because a BUG() statement in huge_pte_alloc() attempts to check that a pte, if present, is a hugetlb pte, but it does so in a non-lockless-safe manner that leads to a false BUG() report. We got here due to a couple of bugs, each of which by itself was not quite enough to cause a problem: First of all, before commit c33c794828f2("mm: ptep_get() conversion"), the BUG() statement in huge_pte_alloc() was itself fragile: it relied upon compiler behavior to only read the pte once, despite using it twice in the same conditional. Next, commit |
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README |
Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.